Device for testing at least one quality parameter of a fluid

ABSTRACT

The invention relates to a device for testing at least one quality parameter of a fluid in fluid apparatuses, e.g. working cylinders ( 10 ), hydraulic accumulators, valves, filter housings, pressure tubes, which at least temporarily accomodate a given fluid volume in at least one fluid chamber ( 12, 14 ). Said fluid volume is stored in a storage unit ( 16 ) with the aid of a control mechanism ( 16 ) after being discharged from the fluid apparatus in order to be redirected from there into a measuring element ( 22, 24 ) to verify the respective quality parameter of the fluid. The inventive device makes it possible to specifically obtain a statement about the operability of the respective fluid apparatus within a very short period of time.

The invention relates to a device for testing at least one qualityparameter of a fluid in fluid devices such as working cylinders,hydraulic accumulators, valves, filter housings, flexible pressuretubing, etc.

Subsequently published DE 102 47 353 discloses a process for reducingthe flow dependence of measuring instruments for determination ofimpurities as indication of the quality of a fluid, especially solidimpurities such as particles in fluids, by means of a particle countsensor operating in particular on the basis of the light blockingprinciple and mounted in a measuring cell of the measuring device, whichhas a specifiable input cross-section for the flow of fluid, the sensorgenerating a light beam cross-sectional area over which the flow offluid is conducted for detection of an impurity. Particle count sensorsoperating on the light blocking principle determine the relativeproportion of the light beam cross-sectional area (perpendicular to theoptical axis) which is covered by projection of a pollutant particle inthis plane.

DE 198 60 169 A1 discloses a process for qualitative determination ofsmall amounts of water in multicomponent systems in the liquid state ofaggregation, oil in particular, the process being characterized byrepetition of the following process steps several times:

-   -   incomplete extraction of moisture from the multicomponent system        by means of a carrier gas;    -   quantitative determination of the amount of moisture extracted        by measurement of the relative humidity in the carrier gas, the        carrier gas volume, and the temperature; and    -   conversion to the amount of moisture of the multicomponent        system after determination of the mass of the multicomponent        system and the saturation vapor density in the carrier gas.

The disclosed process and device provide the possibility of measuringthe absolute saturation concentration of moisture in fluids such ashydraulic oil, the parameter determination in question in turnpermitting formulation of a statement regarding the quality of the oil.

DE 101 52 777 A1 discloses a device for determination of the quality ofa medium, a lubricant and/or cutting oil in particular, having severalsensors which generate an electric output signal as a function of therespective sensor-specific input quantity, one sensor being atemperature sensor which generates an output signal which is a functionin essence exclusively of the temperature of the medium and isessentially independent of the quality of the medium, and at least oneother sensor generating an output signal as a function both of thequality of the medium (fluid) and of the temperature of the medium. Thesensors in question are in the disclosed solution mounted on a commonsubstrate immersible in the fluid, so that the measuring devicedisclosed is mounted in a very small structural space.

The disclosed measuring devices and processes indicated in the foregoingmake available a very good set of instruments for determination ofquality parameters for fluids, including media in the form of a gasand/or paste. The respective measuring devices may also be supplementedby chemical analysis processes, for example, in order to arrive atdeterminations regarding free radicals in a hydraulic oil, temperature,viscosity, pH value, electric conductivity, etc. Such devices entail aprolonged measurement or determination period depending on the measuringprocess employed, along with the associated measurement device anddepending on the quality parameters of the fluid to be determined. Outof consideration of reasons of process accuracy, length of themeasurement period, and the validity of the test result it has beenfound to be advisable to use such quality measurement processes directlyon test stands where the operation of fluid devices such as hydraulicassemblies, valves, filter housings, flexible pressure tubing, etc., maybe tested. Use of the respective operating fluid is necessary, onlocation, in order to verify the quality of the fluid thus used by meansof the measuring device, if possible simultaneously with testing of theassembly. In this way determination is made of the suitability of therespective fluid device for subsequent operation in order, in turn, toobtain a broader indication of the quality of the preceding productionsteps with respect to the fluid device (assembly) which has been or isto be tested.

On the basis of these considerations, the object of the presentinvention accordingly is to create a device meeting the requirement asoutlined. The object as thus defined is attained by means of a devicehaving the characteristics specified in claim 1 in its entirety.

The device claimed for the invention for testing at least one qualityparameter of a fluid of fluid devices is characterized in that at leastoccasionally a specified volume of fluid is received into at least onefluid space of a particular fluid device and, after leaving the fluiddevice, may be stored in a storage device by means of a control devicein order subsequently to be fed further to a measuring device fordetermination of the respective quality parameter of the fluid to bedetermined.

If a fluid device has been produced, for example, in the form of workingcylinders, hydraulic accumulators, valves, filter housings, flexiblepressure tubing, etc., and is placed on a testing stand, the functionaltesting generally has been preceded by a plurality of production stepsinvolving machining to some extent, something which usually results infouling of the fluid spaces of the respective fluid device. Foulingoccurs even if no machining has been carried out, either in the form ofdust or in the form of operating media such as corrosion protectionmeans, lubricants, other hydraulic media, etc. If delivery is then madeto customers, after appropriate functional testing, in which theoperating fluid is admitted to the respective fluid device, foulingmatter remaining in the fluid spaces could impede subsequent operationand result both in failure of the respective fluid device and failure ofall-hydraulic unit, even if such units are additionally protected byfilter devices or the like.

It has been found in practical applications that the danger in questionmay be reduced if on the test stand the fluid medium is applied to thefluid spaces of the fluid device involved several times in a sort ofscavenging process and the spaces are then emptied of the fluid mediumin order to obtain a yield at least of fouling particles. However, evenif a very high number of scavenging processes are carried out thepossibility cannot be excluded that in a special case fouling materialmay remain in the fluid space and then result in the adverse effectsindicated in the hydraulic circuit in subsequent operation of the fluiddevice. In order to prevent such occurrence, it is claimed for theinvention that, after the scavenging cycle has been completed, the lastamount of fluid introduced is subjected to thorough testing by theappropriate measuring device. If the fluid space is small because of thegeometric dimensions of the respective fluid device, the volume of fluidinvolved may be taken directly to the measurement device for onlinemeasurement if the amount of fluid present in the fluid space issufficient for such online measurement; otherwise the amount of fluidrequired for reliable online measurement may be collected and madeavailable by the device claimed for the invention. With fluid devices oflarge dimensions in particular, however, the fluid volumes of the fluidspaces are also large, so that with the online measurement process asoutlined a very lengthy measurement period elapses before the entirevolume of fluid is tested, with the result that the test stand continuesto be occupied and may not be used for testing of another fluid deviceto be introduced into the test stand. The invention is introduced atthis point and takes from the large amount of fluid the amount requiredfor online measurement. The device claimed for the invention isespecially well suited for applications in which only brief testing ormeasurement periods are available. The measurement stand itselfaccordingly assumes very high measurement cycles and amounts of fluidwhich depart from the optimum measurement volume, for example, becausethe amounts of fluid employed are very small or very large.

The device claimed for the invention now makes it possible for theamount of fluid of the last scavenging cycle to be introduced by meansof a control device into a storage device and from the latter the fluidto be tested may be moved on to the measuring device, the control devicesimultaneously permitting change of the fluid device to be tested on thetest stand. Replacement of the fluid device may accordingly beundertaken while the measurement (testing) proper for the precedingfluid device is still in progress. Hence, the device claimed for theinvention is especially well suited for quality parameter checking influid devices if large volumes of fluid are to be tested and/or onlybrief measurement periods are available for this or other reasons.Because of the intelligent configuration of the control device,preferably as microprocessor equipment, it is possible to use fluiddevices having fluid spaces of small dimensions to conduct onlinetesting or testing after a prescribed delay period, it being possible touse the measurement period in question to effect the desired replacementon the test stand. The device claimed for the invention accordinglyhelps in lowering the expenditure of time and costs and, because of thesolution applied, may be suitably employed in a multiplicity ofembodiments.

By preference the storage device in question consists of a workingcylinder, in particular one in the form of a pneumatic cylinder whichmay be connected on the piston side by way of a feed line so as toconduct fluid to the associated fluid space of the fluid device by meansof the control device, the measurement device being mounted in thedirection of flow of the fluid beyond the working cylinder in adischarge line. If the volume of the storage unit is sufficiently large,if desired several quantities of fluid may be stored for severalconsecutive rinse cycles and then recalled for the overall measurement.This permits a statistically improved, firmly established, evaluationand accordingly overall state regarding the quality of the fluid deviceproduced.

The device claimed for the invention may be used in particular to obtaina reliable indication of the fouling status of the fluid to be testedand thus of the fluid device. Should such be desired, in addition todetermination of the number of (fouling) particles, depending on themeasurement device employed indications may also be obtained of thesize, type, and speed of the particles present in the fluid to betested. The respective quality parameter test may be furthersupplemented by other values such as viscosity, temperature, freeradicals, pH values, electric conductivity of the fluid to be tested,etc.

Additional advantageous embodiments are presented in the other dependentclaims.

The device claimed for the invention will be described in what followson the basis of an exemplary embodiment with reference to the drawing,in which there is presented in the sole drawing, in diagrammatic formnot drawn to scale, the structure of the device claimed for theinvention for testing a hydraulic working cylinder after completion of aspecifiable number of testing and scavenging cycles, the hydraulicdevice carrying out the scavenging cycle being omitted for the sake ofgreater simplicity of presentation.

The device shown as a whole in the figure serves the purpose of testingat least one quality parameter of a fluid in fluid devices, such as onein the form of a hydraulic working cylinder 10. A fluid device such asthis at least occasionally receives a specified volume of fluid in atleast one fluid space. In the present situation the hydraulic workingcylinder 10 has a fluid space 12 on the rod side and a fluid space 14 onthe piston side. The respective volume of fluid, after leaving the fluiddevice, in this instance in the form of the hydraulic working cylinder10, may be stored by means of a control device identified as a whole by16 in a storage device. There are associated with the fluid space 12 thestorage device 18 and with the fluid space 14 on the piston side anotherstorage device 20, which is essentially the same in design as the firststorage device 18. The volume of fluid may be moved from the storagedevice 18, 20 to an associated measurement device 22, 24, which servesto determine the respective quality parameter of the fluid. Themeasurement devices in question are essentially equivalent to eachother.

A measurement device 22, 24 such as is described in DE 102 47 353 may beemployed as the respective measurement device 22, 24. The measurementdevice as described carries out a process for reducing the dependence ofthe respective measurement devices on flow for determination ofimpurities, especially fouling by solids such as particles in fluids, bymeans of a particle count sensor, especially one operating on thelight-blocking principle and mounted in a measuring cell of themeasurement device having a specified inlet cross-section for the flowof fluid, the sensor generating a light beam cross-sectional area overwhich the flow of fluid is conducted for detection of the impurity inthe flow of fluid, the light beam cross-sectional area selected for thedirection of flow of the fluid being greater than such area transverseto the point of entry of the impurity into the light beamcross-sectional area.

There is thus obtained a light beam cross-sectional area, preferablygenerated by a conventional laser, of the particle count sensor whichdoes not illuminate the complete cross-sectional area of the measuringcell, but on the other hand is distinctly of greater extent in thedirection of flow, with the result that even markedly small (fouling)particles, such as ones of a size of 2 μm, can be immediately detectedwithout increase in the cost of measurement with the equipment mounteddownstream. An evaluation process suitable for such a particle counteris described in detail in DE 197 35 066 C1 and thus will not be dealtwith at greater length here. However, the device disclosed makes itpossible reliably to detect even the smallest particle. The possibilityalso exists of detecting air bubbles in the flow of fluid in order toarrive at permissible statements concerning the quality of the fluidwhich may also result from different particle geometries.

The respective storage device 16, 18 consists of a working cylinder, inparticular one in the form of a pneumatic cylinder of conventionaldesign, which may be connected on the piston side by way of a feed line26 so as to conduct fluid to the fluid space 12, 14 of the fluid deviceassociated with it by means of the control device 16, the respectivemeasurement device 22, 24 being mounted in the direction of flow of thefluid downstream from the pneumatic working cylinder in a discharge line28. This discharge line 28 extends from the measurement device 22, 24 byway of an adjustable choke 30 to the tank side T of the device.

The working cylinder of the two storage devices 18, 20 has a piston rod32 with a through fluid duct (not shown) which discharges on one sideinto the respective piston space 34 of the working cylinder and on itsother side into a connecting line 36, which in turn may be blocked bythe control device 16. As an extension of the connecting line 36 itdischarges on the tank side T. The rod side 38 of the respective workingcylinder is connected to a compressed gas source 40, in particular onein the form of a compressed air or nitrogen source, this sourceproviding an operating pressure of several bar, such as 6 bar. Inaddition, the movement of displacement of the piston 42 is monitored bya monitoring device 44 as part of the control device 16 with endposition switches.

The control device 16 has switching valves, in particular ones in theform of 2/2-way switching valves 46, 48. The switching valves 46, 48 areshown in the figure in their output blocking position; when in theirother switching position, after they have been operated, they clear thepath for the fluid. These switching valves 46 and 48 clear or close thefluid conducting path for the feed line 26 and/or the connecting line36. The control device 16 uses the output signals of the monitoringdevice 44 in the form of the four end-position switches shown in thefigure to operate the switching valves 46, 48. A pressure control valve50 is connected to the respective feed line 26 to the pneumatic workingcylinder, between the latter and the associated switching valve 46 ofthe control device 16. This pressure control valve 50 in turn leads tothe tank side T.

For the sake of better understanding the device claimed for theinvention will now be described on the basis of a practical application.The hydraulic working cylinder 10 shown in the figure comes from thefactory and undergoes thorough functional testing on a test stand notshown. Since machining processes are also involved in the production ofsuch hydraulic working cylinders, it is to be expected that there may befouling material in the fluid spaces 12, 14 which may also derive fromresidue of cooling lubricants or the like. Before the device is employedin a practical application the hydraulic working cylinder 10 isscavenged, that is, a fluid is alternately introduced into and removedfrom the fluid spaces 12, 14, this serving the purpose of eliminatingfouling material from these fluid spaces. Once such a scavenging cyclehas been completed, first thorough testing is effected by the associatedmeasurement device with the piston in the fluid space 12 retracted onthe rod side. For this purpose, the control device 16 opens theswitching valve 46 and fluid flows over the feed line 26 into the firststorage device 18.

If the switching valve 48 remains closed, the quantity of fluidintroduced into the feed line 26 may serve the purpose of scavengingboth the valve 46 and the measurement device 22, along with the pistonspace 34 of the storage device 18. If the switching valve 48 is closed,fluid is forced under pressure into the piston space 34, the pistonrising to an upper end position which is checked by the monitoringdevice 44. The fluid now present in the piston space 34 is then to bedelivered to the associated measurement device 22 for the examinationfor the presence of particles already described. If, surprisingly, highpressures occur, the proper state of the system is secured by thepressure control valve 50, which to this extent performs a safetyfunction. The control device 16 now closes the switching valve 46 and,as a result of actuation of the compressed gas source 40, pressurizedgas reaches the rod side of the pneumatic cylinder and the piston 42moves downward as viewed in the line of sight to the figure, the lowerend position being monitored by way of the associated end positionswitch of the monitoring device 44.

The fluid displaced by the piston then moves into the measurement device22 by way of the drain line 28 for the particle count indicated andthence to the tank side T by way of the adjustable choke 30. Themeasurement cycle proceeds in a similar manner as soon as the amount offluid in the piston fluid space 14 has been displaced in the directionof the other storage device 20 by return of the piston of the hydraulicworking cylinder 10. If the two switching valves 46 are then in theirblocking position illustrated in the figure, during the particlemeasurement itself by the measurement devices 22, 24 the workingcylinder 10 which has been present in the test stand up to this point isreplaced by a new one, the measurement result for the preceding workingcylinder tested by the measurement devices 22, 24 also being present oncompletion of the replacement. In this way the testing cycle, along withthe testing device, is not harmed and very reliable test results areobtained in this instance by the device indicated.

Nor is it necessary to test each working cylinder. Hence, for example,only some of the working cylinders deriving from a processing seriesneed be tested, by conduct of statistical evaluation processes. Themeasuring device used for the purpose is suitable in particular forfluid devices, such as large hydraulic working cylinders 10 having fluidspaces 12, 14 with large volumes. As a rule, the possibility also existsof introducing several scavenging amounts in succession into therespective storage devices, as a function of the size of the hydraulicworking cylinder 10, and then later of determining their quality bymeasurement. Consequently, the device claimed for the invention isespecially well suited for large volume flows and for measurementperiods available only for a short time.

If the hydraulic device is of small dimensions, and so the fluid spaces12, 14 of a hydraulic working cylinder 10, for example, are of lowvolume, the storage device 18, 20 is also of assistance, so thatmeasurement with the measurement device 22, 24 may be effected onlineduring a process of introduction and removal of a cylinder. In thisinstance the respective switching valve 46 in the feed lines 26 is to beactuated. In the respective online measurement process with low volumesof fluid, the piston 42 of the respective storage device 18, 20 moves toits respective associated position; this may be suitably effected by wayof the control device.

The device claimed for the invention need not be restricted to hydraulicworking cylinders; as a rule, it is suitable for use with fluid devicesof any form into which a specifiable quantity or volume of fluid isintroduced periodically. Consequently, applications for hydraulicaccumulators, hydraulic valves, flexible pressure tubing, etc., are alsoconceivable. Nor need measurement be restricted to particle evaluation:depending on the particular measurement device employed, other data maybe obtained, such as free radicals in oil, pH values, electricconductivity, consistency, viscosity, etc.

1. A device for testing at least one quality parameter of a fluid influid devices such as working cylinders (10), hydraulic accumulators,valves, filter housings, flexible pressure tubing at least periodicallyreceiving a specified volume of fluid into at least one fluid space (12,14), which volume may after leaving the fluid device be stored by meansof a control device (16) in a storage device (18, 20) and then movedfurther from such storage device (18, 20) to a measurement device (22,24) for the purpose of determining the respective quality parameter ofthe fluid.
 2. The device as claimed in claim 1, wherein the storagedevice (16, 18) is in the form of a working cylinder, especially in theform of a pneumatic cylinder, which may be connected on the piston sideby way of a feed line (26) to the fluid space (12, 14) associated withit of the fluid device by means of the control device (16) and whereinthe measurement device (22, 24) is mounted downstream from the workingcylinder in the direction of flow of the fluid in a drain line (28). 3.The device as claimed in claim 2, wherein the working cylinder has apiston rod (32) with a through fluid conducting passage which dischargeson one side into the piston space (34) of the working cylinder and onits other side into a connecting line (36) which may be blocked by thecontrol device (16).
 4. The device as claimed in claim 2, wherein therod side of the working cylinder may be connected to an actuating devicesuch as an electrically and/or hydraulically operated supply source orto a compressed gas source (40), a compressed air or nitrogen source inparticular, and wherein the movement of displacement of the piston (42),in particular such movement relating to the end positions of suchpiston, may be determined by a monitoring device (44).
 5. The device asclaimed in claim 4, wherein the control unit (16) actuates switchingvalves (46, 48), in particular 2/2-way switching valves, for clearing orblocking the feed line (26) and the connecting line (36) and wherein thecontrol device (16) also takes the output signals of the monitoringdevice (44) into consideration for the purpose of the respectiveactuation of the switching valves (46, 48).
 6. The device as claimed inclaim 5, wherein a pressure control valve (50) is connected to the feedline (26) to the working cylinder, between such working cylinder and theassociated switching valve (46) of the control device (16).
 7. Thedevice as claimed in claim 1, wherein a separate storage device (18, 20)with measurement device (22, 24) is provided for each fluid space (18,20).
 8. The device as claimed in claim 1, wherein the measurement device(22, 24) determines in particular the size and/or the number and/or thespeed and/or the type of particles present in the fluid and/or qualityparameters such as viscosity, aging, temperature, pH value, or theelectric conductivity of the fluid.
 9. The device as claimed in claim 7,characterized in that the fluid device is a hydraulic working cylinder(10) which may be connected both by its piston side and by its rod sideto the pneumatic working cylinder and to the associated measurementdevice (22, 24) and in that the control device (16) makes possiblereplacement of the hydraulic working cylinder (10) with a new suchcylinder to be tested, while determination of the quality of the fluidis effected in the respective fluid space (12, 14).